Storm drainage piping is a pivotal aspect of infrastructure. Storm drains take surface drainage below-ground for conveyance to a location where the drainage can be safely discharged along historic paths. Without a storm drainage system, all storm water runoff would remain above-ground flooding structures and making development difficult, if not impossible.
Currently, most common storm drainage pipes are made from either plastic, including high-density polyethylene (HDPE) and polypropylene (PP), or reinforced-concrete pipe (RCP). Plastic pipes have external corrugations and either a smooth or corrugated interior with an anticipated design life exceeding 100 years. Plastic pipe's low weight relative to reinforced-concrete pipe is the biggest advantage of plastic over reinforced-concrete pipe. The lighter weight permits lower haul costs by permitting more pipes to be loaded onto a semi-trailer. Typically, plastic pipes are easier to lay and connect since the pipes can usually be moved manually by laborers, as opposed to requiring heavy equipment to move reinforced-concrete pipes.
Structurally, the downside to plastic pipe is the flared end sections implemented with plastic pipes. The flared end sections are essentially the “mouth” of the pipe that spreads drainage and releases the drainage onto grade. The flared end sections designed for plastic pipe is typically made from HDPE or PP. Plastic flared end sections have thin-walls, are extremely lightweight, and do not have sufficient strength to withstand loads imposed by surrounding soil when the flared end section is backfilled and the pipe is buried. The top and sides of plastic flared end sections will buckle and collapse under the weight of surrounding soil. A second issue with plastic flared end sections is the lack of ability to attach any sort of guard or protective measure, for instance a trash rack, to keep animals and children from entering storm pipes. This is a substantial hazard, especially in locations where small children are present.
Reinforced-concrete pipes are concrete pipes with internal steel reinforcing. Reinforced-concrete pipes have good strength and ability to hold up under heavy loads. However, reinforced-concrete pipes are heavy, resulting in expensive transportation and installation costs. A reinforced-concrete flared end section also has good strength. Further, protective measures including trash racks can be attached to the reinforced-concreted flared end sections.
Plastic pipe and reinforced-concrete pipes generally have different cross-sections, even though their internal diameters are standardized. Reinforced-concrete pipe has a smooth wall both inside and out. Reinforced-concrete pipe can have a wall thickness ranging from 2 inches for a 12 inch internal diameter pipe to 6 inches for a 60 inch internal diameter pipe. Most plastic pipes have a corrugated exterior wall that ranges in thickness from 1.25 inches for a 12 inch internal diameter pipe to 3.2 inches for a 60 inch internal diameter pipe.
Both plastic pipes and reinforced-concrete pipes use bell-and-spigot joints. The bell is the “female” connection portion while the spigot is the “male” connection portion. The varying wall thicknesses between the two types of pipes do not permit a standard connection between the two. Both types of pipes presently utilize watertight gaskets in joints that meet the American Society of Testing and Materials (ASTM) standards. The ASTM Standard F477 is the industry accepted standard for HDPE and PP storm drainage pipe joints while ASTM Standard C443 is the industry accepted standard for reinforced-concrete storm drainage pipe joints.
Flared end sections are not wholly buried like the remainder of the storm drainage pipes. Consequently, their exposure to surface conditions and discharge of the storm water can result in some movement of the flared end section. Therefore, it is an industry standard to provide mechanical restraint to keep the flared end section securely attached to the storm drainage piping.
A coupler and gasket is needed to join a corrugated plastic pipe to a reinforced-concrete flared end section so that the full advantages of both items can be realized.